From 2f7691e26aa305be995f8548a800bc59fb40a7f2 Mon Sep 17 00:00:00 2001
From: Mikolaj505 <61552376+Mikolaj505@users.noreply.github.com>
Date: Mon, 23 Mar 2026 15:45:09 +0100
Subject: [PATCH] fix: Handling mirrored case when applying transform

---
 src/ACadSharp/Entities/LwPolyLine.cs | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/src/ACadSharp/Entities/LwPolyLine.cs b/src/ACadSharp/Entities/LwPolyLine.cs
index 47bfcc6eb..807cfd162 100644
--- a/src/ACadSharp/Entities/LwPolyLine.cs
+++ b/src/ACadSharp/Entities/LwPolyLine.cs
@@ -123,12 +123,27 @@ public override void ApplyTransform(Transform transform)
 
 			this.getWorldMatrix(transform, this.Normal, newNormal, out Matrix3 transOW, out Matrix3 transWO);
 
+			var m = transform.Matrix;
+			double det =
+				m.M00 * m.M11 -
+				m.M01 * m.M10;
+
+			bool mirrored = det < 0;
+
 			foreach (var vertex in this.Vertices)
 			{
-				XYZ v = transOW * vertex.Location.Convert<XYZ>();
-				v = transform.ApplyTransform(v);
-				v = transWO * v;
-				vertex.Location = v.Convert<XY>();
+				// OCS → WCS
+				XYZ transformationVector = transOW * vertex.Location.Convert<XYZ>();
+				transformationVector = transform.ApplyTransform(transformationVector);
+
+				// WCS → new OCS
+				transformationVector = transWO * transformationVector;
+				vertex.Location = transformationVector.Convert<XY>();
+
+				if (mirrored && vertex.Bulge != 0.0)
+				{
+					vertex.Bulge = -vertex.Bulge;
+				}
 			}
 
 			this.Normal = newNormal;